Experiments are proposed to study the involvement of host cell DNA repair functions in cellular transformation by simian virus 40 (SV40). Transformation of the following repair deficient cells will be studied: human cells carrying known or potential repair deficiencies (xeroderma pigmentosum, Bloom's syndrome, Fanconi's anemia), primary baby mouse kidney cells unable to repair ultraviolet(UV)-irradiated polyoma virus, and mouse cells selected in culture for altered responses to UV light or mitomycin C. The involvement of repair functions in transformation will be determined by measuring transformation frequencies, the frequency of integration of viral DNA into the host genome, and the frequency of virus rescue (excision) following transformation with untreated virus of virus inactivated with UV light or mitomycin C. In order to determine whether the action of repair functions early in transformation can affect the ultimate phenotype of the transformed cells, tumor(T) antigen levels and cellular growth properties of isolated transformed cells will be studied. Experiments will also be performed to elucidate the mechanism of viral transformation events involving host DNA repair functions.